title: Hypermethylation of the DPYD promoter region is not a major predictor of severe toxicity in 5-fluorouracil based chemotherapy.
abstract: BACKGROUND
  The activity of dihydropyrimidine dehydrogenase (DPD), the key enzyme of pyrimidine catabolism, is thought to be an important determinant for the occurrence of severe toxic reactions to 5-fluorouracil (5-FU), which is one of the most commonly prescribed chemotherapeutic agents for the treatment of solid cancers. Genetic variation in the DPD gene (DPYD) has been proposed as a main factor for variation in DPD activity in the population. However, only a small proportion of severe toxicities in 5-FU based chemotherapy can be explained with such rare deleterious DPYD mutations resulting in severe enzyme deficiencies. Recently, hypermethylation of the DPYD promoter region has been proposed as an alternative mechanism for DPD deficiency and thus as a major cause of severe 5-FU toxicity.
  
  
  METHODS
  Here, the prognostic significance of this epigenetic marker with respect to severe 5-FU toxicity was assessed in 27 cancer patients receiving 5-FU based chemotherapy, including 17 patients experiencing severe toxic side effects following drug administration, none of which were carriers of a known deleterious DPYD mutation, and ten control patients. The methylation status of the DPYD promoter region in peripheral blood mononuclear cells was evaluated by analysing for each patient between 19 and 30 different clones of a PCR-amplified 209 base pair fragment of the bisulfite-modified DPYD promoter region. The fragments were sequenced to detect bisulfite-induced, methylation-dependent sequence differences.
  
  
  RESULTS
  No evidence of DPYD promoter methylation was observed in any of the investigated patient samples, whereas in a control experiment, as little as 10% methylated genomic DNA could be detected.
  
  
  CONCLUSIONS
  Our results indicate that DYPD promoter hypermethylation is not of major importance as a prognostic factor for severe toxicity in 5-FU based chemotherapy.
authors.affiliation: Institute of Clinical Chemistry, Inselspital, Bern University Hospital, and University of Bern, CH-3010 Bern, Switzerland. ursula.amstutz@insel.ch
authors.forename: Ursula
authors.initials: U
authors.lastname: Amstutz
authors.forename: Simone
authors.initials: S
authors.lastname: Farese
authors.forename: Stefan
authors.initials: S
authors.lastname: Aebi
authors.forename: Carlo R
authors.initials: CR
authors.lastname: Largiadèr
mesh_terms: D000368:Aged; D000964:Antimetabolites, Antineoplastic / Q000627:therapeutic use / Q000633:toxicity*; D019175:DNA Methylation; D042943:Dihydrouracil Dehydrogenase (NADP) / Q000235:genetics* / Q000378:metabolism; D005472:Fluorouracil / Q000627:therapeutic use / Q000633:toxicity*; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000188:drug therapy* / Q000201:enzymology* / Q000235:genetics; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic
chemical_list: D000964:Antimetabolites, Antineoplastic; D042943:Dihydrouracil Dehydrogenase (NADP); D005472:Fluorouracil